Seismic prospecting system



March 25, 1952 G. M. GRoENr-:NDYKE SEISMIC PROSPECTING' SYSTEM Filed March 10, 1948 9 Sheets- Sheet 1 March 25, 1952 G. M. GRENENDYKE 2,590,530

SEISMIC PROSPECTING SYSTEM March 25, 1952 G. M. GROENENDYKE SEISMIC PROSPECTING SYSTEM 9 Sheets-Sheet 3 Filed March l0," 1948 /V 'Il EEE 4 6 vvv m A March 25,'1952 G. M. GROENENDYKE slush/Irc PRosPEcTrNG SYSTEM 9 Sheets-Sheet 4 Filed March l0, 1948 Y Tqi.

March 25, 1952 G. M. GRQENENDYKE 2,590,530

SEISMIC PROSPECTING SYSTEM 9 Sheets-Sheet 5 Filed March 10, 1948 7 INVENTOR E. Goff/vf M. lG/Faf/Vf/t/f/rf ATTO EY sEIsMIc PRosPEcTNG SYSTEM. Filed March 1o, 1948 9 sheets-sheet e ATTO R Mlch 25, 1952 G. M. GROENENDYKE .2,590,530

SEISMIC PROSBECTING SYSTEM 9 Sheets-Shael'. 7

Filed March l0, 1948 March 2S; 1952 G. M. GROENENDYKE 2,590,530

SEISMIC PROSPECTING SYSTEM Filed March 1o, 194e 9 sheets-sheet a March 25, 1952 G. M. GRo'L-:Nl-:NDYKE SEISMIC PROSPECTING SYSTEM 9 Sheets-Sheet 9 Filed March 10, 1948 Patented Mar. 25, 1952 aseasso" e New York I l This invention-relatesto geepliyfsical -'ros ing and more partiou-larlylto''sei areas covered by water, as and has for anj objctth'e pro s and apparatusfforl carryingv on su a minimum of time" and" dufrng rough weathe conditions that would otherwise nec'ssit e cessationA of operations Due to the generally' aeepted knowledge that-'therev ares'l'bs't'antial'oi or' pie-1 troleum deposits coastalY are sf cov water, it has become inost-'d seismic surveys forsub-surface Iapp areas in order to locate charaCteri'stwl s 'u'b-- face formationsl which pro'videf tii no'st lilffeiy'y locations for the drillingofwells".

The difficulties encountered inE iiduetinglseismic surveys in" submerged areas vlilrlieal l' parent whenv it is" consideredthat? sesriiieJ d i tectors must" be' p la'cedA along' a@ predete d" line at predeterminedf itervalsandorien a' predetermined position atfe'ac'hf loca'tior'falong that line. The geophones'm'omprisiigasprje'dI-- in conformance to techniques? used onf' landare' usually located" atre'gularly spaced points'falongfthe line and'mustbe oriented-inisuchfa-positln; usually vertical, that' the instantanefus`V voltage'4 of a geophone willbe-off theproperv polarity"withV respect to the' seismic 'Wavestoberecrdedand: of the same polarity as"theother? geophonesof: the spread; Further', aspre'a'd'off g'aup'hones;-v as' used in presentA day seismograph-practi'ce toproduce a` record, comprises at;-'1easttwo-geophes' per tracealthough 'itisf'often preferableto-util-ize-I a number greater than this inorder tofeliminatenear-surface eiects. This means,- that` theiij spread, in order tol produce' a usefulfrecordfofsixl or seven traces,- willcomprise twelve, fourteen;- or more geophones,- each ofgwhichmust be positioned at predeterminedv locationswith respect` to a line alongwhichthe' seismic surveyisl-being conducted.

Further, it is necessary toA prov-ideggeophonesj in which they operating parts-aregiiud sealed; a pair of insulatedr conductors extendingfyfrom each geophone tothe assoeiated'- reccgrdingdnfy struments, and some means and/ 1' metho"c i by which each of the geophqnes'maybefplaeedat some predeterminedpointin orion the water in such a positionthat the geophones willbe sensitive to the seismic Waves tojbe'recorded There have been severaldiiiferent'approaches to the problem. Three ofY the suggestedpsoluf tions are characteriaed" respeetivel' boat; (2) suspending. eachgeophoiie frein boy (c1. Erlasse) 2'4 on; alom-frequency system at some intermediate depth, and (3) providing means whereby the geophgn'es.' uponremoval of a towing force will descend to, and rest upon, theocean floor. The desirability o f having a set of geophonesl andltheinassoeiated conductors so arrangedthat they niay be `towed from; spread to spread has' been' recognized. However, in such systems there havebeen no provisions'to take care of twisting and rotation, and ingeneral there have. been lacking provisions to prevent failure of geoph'onesbecause of improper positioning or entanglement with the associated cables, etc.

It' isf,I therefore, an object in the present in veritior"4 to' provide apparatus for seismograph siiri'fey's iii-areas'l covered by Water which will' as' sure accurate and rapid location' of each of the geoplio'nes in the spread and at the Sametime whielrautdmatically will orient' the geophones irisih a position thatl they will be se'hstiveto the seismic' signals to be recorded. A further object of the invention is to provide cable-geophone'units in which each geophone casef'c'oniprises a part'of' the cable, i. e.; a

junction box therefor, and as such serves"bothr as-ja" coupling' box for transmission therethrough of the`Y towing' force and for separate passage therethrough of the elebtr'ical'conductors. isa-further object` of the invention to provide' surveyingn apparatusv in which each geo# phone and its housing or ,casev comprises an in tegral'part'of the cable,I their relation preferabl being such that the axisof the cable and'of'the geophone caseare colin'eai. f

It isaurther" object'of the'pre'sent invention vtofprovide an'l underwater. surveying apparatus with self-contained geophon'es, conductors and towing cable of mechanical strength great enough forl dragging or towing the .same from oneioeation-to another without requiring further adjustments or operationsv with respect there` tobutiwhich is alwaysfin condition forreception off V seismic impulses and transmission of gen-'- erated electrical/impulses g from the `geophon'esv to" the re'eor'ding'v unit -and which resists any" abra;-

si'onwhiohmay beincurred by dragging the cable unit alongl the ocean oor, as over or through towed or dragged over the surface lto besurvy'ed, wi11 p1a ntv itself in intimateecnb' tactwith 'the surfacejto; provide efficient transfer" of' s"eis"mic' v energy from the surface to the" t er object is'toprovide 'apparatus which,l

clucles the cable-circuit selecting means forming the subject matter of a concurrently led application by Kenneth W. McLoad, Serial Number 14,155, and assigned to the same assignee as the present application. The McLoad improvement has been included herein in order to show the best form in which the invention has been used at the time of filing this application.

For further objects and advantages of the invention, reference shall now be had to the following description taken in conjunction with the drawings in which:

Fig. l is a sectional view of a submerged area illustrating an embodiment of the apparatus of the present invention employed in underwater surveying operations;

Fig. 2 is a sectional elevation of a part of the apparatus in Fig. 1 including a geophone unit and a portion of the cable connector assembly, all but two of the electrical conductors being omitted;

Fig. 3 is an exploded view of a gimbal mounting provided for the detector unit of the system of Fig. 1;

Fig. 4 is a sectional view of the construction of the cable connector assembly at the left of Fig. 2;

Fig. 5 is a sectional view of a modied `form of a cable connector assembly;

Fig. 6 is a sectional view of Fig. 2 taken along line 6--6;

Fig. 7 is a sectional view of Fig. 2 taken along line 'I--'I;

Fig. 8 is an enlarged sectional view of the left end of geophone unit and the cable connector assembly of Fig. 2 with the attachment of the conductors illustrated; A

Fig. 9 is an exploded view in perspective of the geophone case and the cooperating end assembly of a length of cable with certain parts omitted;

Fig. 10 is a modied form of apparatus of Fig. 1;

Fig. l1 diagrammatically illustrates the cable of Fig. 10 showing one way in which the geophones may be connected;

Fig. 12 is an enlarged view of a section of the right end of those portions of the cable which houses geophones I9 and ISA;

Fig. 13 is an enlarged view of a section of the left end of those portions of the cable which houses geophones I9 and ISA;

Fig. 14 is an enlarged view of the righthand end of geophones I4 and I4A;

Fig. 15 is an enlarged view of a portion or the lefthand end of geophones I4 and I4A; and

Fig. 16 is a perspective view of the geophone unit of Fig. 2 mounted in a double gimbal arrangement.

Referring to the drawings, there has been illustrated in'Fig. 1 a simplified embodiment of the:

invention in location in an area in which a seismic aftenincludes tension elements to give to the cable adequate strength to withstand the maximum tensional forces capable of development by: the boat I0. and the electrical conductors which,

complete electrical circuits to the geophones which comprise the spread. Seven geophone units or assemblies I3-I9 are shown in Fig. 1, although it is to be understood that the spread may consist of any desired number of geophone units such as the previously mentioned twelve, fourteen, or more units. For the purposes of clarity and simplicity in the explanation of the invention the simple Z-geophone spread has been illustrated. For the same reason, it will be assumed in the following description that the sienals from the seven geophones I3-I9 are to be transmitted unmixed to the recording instruments carried by boat I0 Where the signals will be recorded on seven traces. In the recording instruments the signals may be mixed or may be recorded unmixed, as desired.

As is well understood by those skilled in the art, seismic surveying may be conducted by positioning the geophones comprising the spread at predetermined locations along a line, ordinarily straight, over which the survey is to be made. With the geophones positioned, as in Fig. 1, an explosive charge, such as dynamite suitably located with respect to the spread is detonated to generate seismic waves. Where the survey is to be conducted in areas covered by water, it becomes feasible to lower from the shooting boat I I a charge 20 of dynamite to the underwater bed or bottom, the weight of the water itself providing the necessary tamping. Upon exchange of proper signals between the recording boat I and the shooting boat II, the charge of dynamite 29 is detonated to generate the seismic waves which thereupon travel downwardly through the earth. Upon reaching an interface or boundary of two sub-surface strata of diflering properties, a part of the seismic energy is reilected. The paths of energy traveling to and reflected from the interface 2I have been indicated by the lines 22, while the travel paths of energy traveling to and reilected from the interface 23 have been indicated by the lines 24. As

`the reflected energy arrives at the geophones I3-I9, seismic signals are generated by each geophone which are transmitted to the recorder by way of the conductors included in the cable i2. The time required after the detonation of the charge of dynamite 20 until the completion of the recording period is of the order of a few seconds. Since this time is so short, it will be readily understood that there is great economic value in any system which will reduce the time boat It), and at a predetermined location there is' lowered to the underwater floor or bottom a further charge of dynamite which will be detonated and further seismic records made. While the shooting boat I I remains at its new location,

' the recording boat I0 will then move forward,

towing and dragging the surveying equipment forming a part of the cable I2 after it until a new and predetermined position is reached. All geophones are at all times properly spaced, properly oriented and when stationary are immediately ready to receive seismic signals for the recording of data resulting from the detonation of succeeding charges from the shooting :boat II in its newly anchored position.

From theforegoing, it willbe seen that in accordance with the present invention there have underwater surveys. Relatively large boats may be utilized, particularly those which are sea-.- worthy Venough to withstand waves of substanf.- tial size Vand'which, as far as the recording boat I8 is concerned, may have power enough to drag vthe spread through a muddy bottom, one of sand, or one including shell reefs. Thus,v with the larger boats the underwater survey may be continued though the weather be too 'inclement for the use of smaller craft which heretofore have been required for individual placement and connection'of geophones veach time the spread has been moved from one location to another. ',Ihere have wholly been avoided branches extending from a cable, which branches are subject to entanglement with submerged objects and reefs and which greatly impair, if not render impractical, the dimore detailed discussion of the manner in which the remaining conductors extend through the housing 29 will :be later referred to, particularly in connection with Figs. 6 9.

The conductors 33 and 34 are connected to plugs 35 and 36 carried by and supported from a ring 31 of electrical insulating material which is itself secured to the plug housing- 21 by means of screws 38. Plugs 35 and 36 are illustrated as rect towing of the surveying apparatus from one location to another, These advantages have proven so great as to suggest the desirability of utilizing the equipment for surface surveys on land and in avoidance of the previous methods o f manually locating the geophones at fixed distances and the need manually to pick them up each time the spread is to be moved. It is to be understood that the invention, as set forth in at least some of the claims, is to include applications either to surface surveying or to underwater survering.

`In accomplishing the foregoing objects and advantages, the cable I2 with the associated geophone units I3-I9 form what, in use, may be considered as a unitary structure, that is to Say, the assembly as a whole may be treated as a length of a cable which may be wound and unwound from a drum, and yet upon being lowered to the bottom or ocean floor, each geophone or seismic detecting device automatically Orients itself for the detection of seismic signals with the proper polarity and with the same polarity as each of the other geophones in the spread. With the foregoing general understanding of the invention and the manner in which it operates, reference Will now be had to the detailed drawings, particularly Fig'. 2 which is a sectional View of that part of the cable I2 which includes the geophone assembly or geophone unit I4. Y 1

Referring to Fig. 2, section ISB of the cable I2 between the geophone assembly I4 and the assembly `I5 has been terminated at the right of Fig. v2 in a plug housing or closure member 21, which is'shown in detail in Fig. 5. The plug housing, as shown in both Figs. 2 and 5, is provided witha flange 21a which, by way of a series of bolts 28, is attached to a flange face of the housing 29 in which a seismic wave detector or geophone 30, Fig. 2, is mounted. The housing 29 is provided with an opening, best shown in Fig. 9, through which parts may be introduced in construction. A lid 29a, is fastened to the case 29 by bolts 29h with gasket 29e effecting a watertight seal as shown in Figs. 2, 6 and '7. To provide a watertight seal at the junction of plugsl 21 and the ends of housing 29, a gasket 3i is provided between the flange face of housing 29 and the flange 21a. The electrical conductors are carried in an insulating jacket or cable 32 which may be of rubber or other suitable exible insulating mavterial. In Fig. 2 only eight of the fourteen lead wires or` conductors 'of cable 32 appear, two of them, the conductors 33 and 34, serve to complete connections tothe detector or geophone 30. Al`

nesting within and making good electrical contact with jacks 40a and 4Gb carried in an electrical insulating member 39 fastened in the end of housing 29 by spring 39a. From the jach 40h .a conductor 42 is electrically connected to a rectangular shank of a spring-biased contact plunge. er 43 supported in a flanged cylinder 44 which is attached to a bearing support 45 of insulating material, as by screws 46. A spring 41 within the closed end of the cylinder 44 urges the contact plunger 43 against a butt contact 48 carried in an insulating member 49. From the contact 48 connection is made by conductor 5U to the sensitive elem-ent of the detector or geophone 33. lConnection to the other terminal of geophone 3D is by way of conductor 5I and through a like assembly including a butt contact 52 and a springbiased contact plunger l53 and thence by conductor 54 to a jack 55a and to a plug 55 to which is connected a conductor 51 of section 54B of the cable I2.

It will be observed in Fig. 1' that each geophone unit or assembly forms in the cable I2 a bulge or enlargement, but not one either of length or of diameter too great to prevent the handling of the cable as a whole as by a reeling drum or the like. NotwithstandingI the compactness of the geophone assembly, there are incorporated therein provisions for assuring that the detector unit or geophone 30 will always be in a position for the most favorable reception of seismic signals. In dragging or towing the cable I 2 along the bottorn of the submerged area being explored, the

cable may tend to rotate about on its longitudinal axis. The invention provides, however, that each detecting unit will remain oriented and will be maintained in a vertical position, whether swivels be included in the assembly between geophones or omitted therefrom. Referring to Fig.v 2 and the exploded view Fig. 3, this is accomplished by supporting the geophone unit 30 in a cradle 58, the lower end of which, as viewed in Figs. 2 and 3, is of heavy construction tc position well below the axis of rotation of shafts 62 and 53 the center of gravity of the assembly, thus to impart to the geophone 33 and the cradle 58 a strong gravity bias which, in the manner of a pendulum, maintains the geophone 30 in a vertical position. Preferably, the cradle 58 is supported by antifriction bearings, illustrated as ball bearing assemblies 68 and 5i, the assembly 58 being carried by bearing support 45 of insulating material, while the bearing 6I is carried by the insulating support 45a. The supports 45 and 45a are mounted on angular ribs 59 by bolts 59a, as shown in Fig. 6.

It will be observed the cradle 58 is provided with cylindrical extensions o-r center-bored shafts 62 and 63 which are pressed into the innervrace of the respective ball bearing assemblies B0 and 6I, each cylindrical extension having pressed therein lan insulating bushing, such as the bushing 43 for the contact 48. It is to be further observed that the axis of the cylindrical extensions or stub-shafts 62 and 63 isin line with, or coaxial of, the cable I2. "Ivhe seismic detector or geo 7 `phone 30 is provided with its own housing, generally hermetically sealed (Fig. 11) with terminals extending therefrom for connection to the conductors 50 and 5I of Fig. 2. The cradle 8, as best shown in Fig. 3, is generally cylindrical in shape, closed at the bottom and has an inner diameter of a length to receive therein the housing of the geophone 3B. In the illustrated form of the invention the lower end of the geophone 30 has one end 30a of reduced cross-section, and the cradle 58 is provided with 'a reentrant opening 53a which serves to form a seating ledge for the larger diameter section of the geophone housing. The geophone is clamped into the cradle by means ci a ber clamping member 64 through which there extend clamping bolts 65, Figs. 3, 1 and 8.

It is quite apparent from Figs. 2, 3, 'land 8 that since most of the mass of the heavy brass cradle and geophone assembly is below the pivotal axis, the position of the center of gravity is well below that axis, thus capable of developing considerable torque. Since the spring-biased friction contacts are small in area and effective at ashort radius, the frictional torque or drag caused thereby is negligible and the geophone 30 will always take a position with its longitudinal axis vertical, regardless of rotation of the cable and housing about their common longitudinal axis. This automatic positioning of each geophone 33 occurs even though the geophone housing 23 may not itself 'be horizontal. Thus, as shown in Fig. l,

all of the geophones are more or less inclined to the horizontal with the exception of geophones I3, I5 and I8. Nevertheless, in all of the remaining geophone units each geophone or detector will be positioned by its own cradle so that it is generally vertical, and in all cases each geophone responds to the arrival of seismic waves with the same polarity as every other geophone.

It has been found in practice that considerable inclination to the horizontal may be tolerated with a geophone without material impairment oi' the character of the records secured. From the practical standpoint, it has been found that the single gimbal support suffices, and the use of the single gimbal support lends itself to -a more compact construction, thus decreasing the size of the housing I4, IIhe smaller the housing I4, the easier the surveying apparatus as a whole may be handled. However, where field requirements dictate, or for other reasons, it is to be understood that a double-gimbal arrangement, such as shown in Fig. 16, may be utilized so that each detector or geophone will always be disposed with its longitudinal axis vertical regardless of the degree of inclination from the vertical of housing 29.

The detector or geophone 30 may itself be of any suitable type, depending upon the character of the survey undertaken and the type or design of recording equipment with which it is used. For example, it may be of a well known velocity type such as the one illustrated in Fig. ll. However, either the displacement, velocity or acceleration type may be utilized as the vibration-sensitive device or seismic detector 3B.

With the foregoing understanding of the construction and arrangement of the parts within the geophone unit or. assembly I4, it will .be understood that each of the remaining assemblies I3 and IE--IQ is similarly constructed and that the electrical connections thereto pass throughout the length of cable I2 and extend from the rear of the boat Ito the recording instruments carried therein. In Fig. 2 only eight of the multiple conductors of the cable appear, two of which, the conductors 42a and 54a, extend through the case 29. For a seven-geophone spread, there will be at least fourteen separate conductors, each insulated from the other and extending the full length of the cable from the boat I0 to the geophone assembly I3. While it would be pos-sible to terminate two conductors in the assembly I9, to terminate two additional conductors in the assembly I8, etc., to the last assembly I3, it is preferred to have all conductors extend through the entire cable. Thus, all of the intermediate sections of cable respectively disposed between adjacent geophone assemblies are of like construction. Similarly, each geophone assembly is of like construction, which means that any particular section may be removed and another like section substituted therefor. If greater spacings are desired between adjacent geophones, l-onger interconnecting cables are substituted for the shorter ones.

Thus, the interchangeability and exibility afforded adapts the surveying apparatus as a whole to any conditions which may be encounteredin the eld and imparts to it the same degree of flexibility that is had with equipment of the type previously used on land. As has here-.- tofore been mentioned, the cable I2 includes as an integral part thereof an inner electrical cable which consists of the electrical conductors embedded or implanted in the continuous rubber jacket 32. In the form of the cable shown in Fig.5 the electrical cable 32 has wound about it a plurality of wire ropes 66. The wire-wrapped cable has an outer cover 61 of abrasion-resistant material such as fabric reinforced rubber, either natural or synthetic. The covering 61 is terminated at the juncture of each cable section and geophone assembly, as at a barbed end of the fitting 68, a plurality of turns of wire 69 being effective tightly to hold the outer cover 61 in place. The Wire ropes 6B extend inwardly through the tting 68 and terminate at a ring 10 to which they are suitably secured as by soldering, spotwelding, or the like. The lefthand end of the fitting 68, as viewed in Fig. 5, is threaded into an extension of the plug housing 21. Between a shoulder 21o of the plug housing and the tapered inner surface 68a is a wedging member 1I, the lefthand end of which abuts against shoulder 21h. Preferably the fitting 68 in the region indicated by the reference character 12 is made hexagonal or square to receive a wrench or other tool tightly to force the tting 68 into the plug housing 21. When this is done, the wedge 1I is driven tightly against the wire ropes 66. In this manner the wire ropes 66 are firmly and frictionally connected to the plug housing 21 which, it will be remembered, is in turn bolted to the housing 29 of the geophone assembly I4.

With this construction, as each cable section enters a geophone assembly, there is a divorcement between the tension members and the electrical members, the latter thereby being protected against application thereto of any towing forces applied to the tension members of the cable by boat III. While it is intended that the cable at the barbed end of each of the fittings 68 will be watertight to prevent ingress of seawater, additional protection is provided for the electrical circuits in the geophone and plug assemblies by the provision of a plurality of sealing members 13 shown in the form of rubber washers. They are disposed centrally of the plug housing 21 between the metallic Washers 13a. When compressed by a nut or compression member 14 which threadedly engages the housing 21, the rubber washers 13 expand to form, with the electrical cable 32 and with the plug housing 21, a wholly watertight seal.

While the form of cable and cable connector shown in Fig. is preferred and may be utilized on each end of each cable section, other forms may be, and have been, utilized. For example, the cable connector shown in Fig. 4 has been found satisfactory and is of the type which may be readily fabricated without special equipment as is required for the assembly of Fig. 5., To minimize the number of drawings, the arrangement .of Fig. 5 has been shown on the righthand side of Fig. 2, while the assembly of Fig-4 has been shown'on the lefthand side of Fig. 2.

Referring now to Figs. 2 and 4, the towing forces are transmitted from the housing 29 through a plurality of Vbolts 28 to the lefthand plug housing 21. In this case, insulated electrical `conductors 16 are molded or vulcanized into a plug 11 of rubber or the like which, with the sealing members 13 and 13a and the nut or compression member 14, forms a watertight connection. In the form of the cable of Fig. 4, the conductors 16 extend through the outer cover 61 together with a braided wire cable 18. The cable 18 is .terminated within a wedging member 88 which rests within a fitting 8l and against a -shoulder Bla thereof. The wedging member l8f3 has a tapered socket through which the end of the cable 18 extends. The end of the cable 18 is held in place by the wedge 82 which is shown as welded or brazed to the cable 18. Preferably, before the brazing operation the strands of cable 18 are spread outwardly, and in the brazing or soldering operation they are integrated into a mass to form the wedge-shaped end .82 whose configuration is complementary to that of the tapered socket of member '80. Any tensional force exerted on the cable 18 tends to press the wedge-shaped end 82 and the wedging member 80 more firmly together. slack in the wires 16 as they enter plug 11 insures that the wires will not be subject to tensional forces. Thus, from the plug housing 21, the towing forces are transmitted through the The provision of some '45 threaded end Blb of the member 8l and thence through wedging member 80 to the wedge-shaped end 82 of cable 18, and thence through cable 18 to the remaining geophone assemblies of the surveying apparatus. It is, of course, apparent that the assembly of Fig. 4 may be utilized in lieu of the one of Fig. 5. the important thingbeing that in any particular surveying equipment all plug assemblies shall be of such uniform construction as will provide interchangeability.

With either cable arrangement of Fig. 4 or Fig.

5, a towing force of any desired magnitude may be applied to the several geophone assemblies without exertion of forces on the electrical cables,

and thus the surveying equipment may be moved readily and quickly from one location toan'other.

There has already been mentioned the fact that the electrical circuits are continuous from one end of the cable to the other. The manner in which the electrical conductors are continued through the cable has been illustrated with particular reference to the conductors 42a and 54a of Fig. 2 and is best shown in Figs. 8 and 9; jIn Fig. 8, which is an enlarged sectional eleyation of the lefthand plug and jack assembly of Fig. 2 there is shown in detail the mannerinwhich'the conductors are attached to the jacks carried in IU the insulating member or disc 39. At a mounting clamp 83 the individual conductors are separated and each individual ywire is connected to one of the jacks carried by the insulated disc 39. The two insulating discs 39 located at the right and the left of each geophone assembly, as viewed in Fig. 2', are of identical construction, and the wires or conductors extend therebetween to like locations; that is to say, the same conductor will be connected to the lowermost jack, i. e., 40a and 55a, in the two discs 39 at the opposite ends of each assembly. As shown in Figs. 6 and 7 and in the exploded view of Fig. 9, the conductors including 42a, and 54a may be laid side by side against the inner wall Aof the housing 29 and held there as by clamps 83 of Fig. 8. The six conductors -which vappear in the right vof Figs. 6 and 31 appear in Fig. 9 in the cutaway section. As previouslygdescribed, the detector or geophone 30 is electrically connected by conductor 50, contact assembly 48, 43 and by conductor 42 to the jack 691i at the righthand end of Fig. 2; and by conductor 5l, contact assembly '52, 53 and by conductor 54 to the jack 55a at the lefthand end of Fig. 2. The jack 40h is connected by the conductor 42a to the jack 55h. Similarly the jack 55a and the jack 40a are interconnected by conductor 54a. It is to be understood that the jacks 39a and 4Gb are located in the supporting disc (not shown) located at the righthand end of Fig. 9 in the same radial positions as corresponding jacks 55a and 551i carried by disc 39. In like manner the remaining jacks at the respective 'ends-of lthe housing 29 are interconnectedso that electrical circuits extend between each pair of similarly located jacks.

In the exploded View of Fig. 9 the geophone coil has been illustrated diagrammatically by a dotted line and is shown connected to the jacks 55a and 55h.l The two plugs 56 and 86 are arranged to be received by the jacks 55a and 55h. Similarly. additional pairs of jacks and plugs serve to take care of the remaining circuits.

Since the plugs and jacks are symmetrically disposed about the axis of the assembly, the plugs may be inserted into any selected jacks, that is the plugs and their cable section may be rotated about the longitudinal axis for movement of plugs 5G and 86 into any selected pair of jacks. Preferably the sensitive element or geophone coil 85 of each geophone is connected to the corresponding jacks of each assembly. The flange 21a may then be secured in the selected position since the bolt holes in flange 21a coincide with those of the housing 29. The advantage of this feature is that ati the factory all coils or pickup units will be connected to jacks in like or identical positions, such, for example, as to jacks 55u-55h, lila-40h of Fig. 2. Each of the pairs of jacks bears identifying characters on the face of the disc or insulating member 39. As shown in Fig. 9, each pair of jacks has been identified by the letters A, B, C', D, E, F, G. 'I'he holes in the flange .of housing 29 are numbered from 1 to '1, these numerals being stamped on the flange, preferably on the peripheral face thereof. In Fig. 9 only the numbers 6 and '1 appear on the peripheral face of the lefthand flange. For the purpose of the following description the other numbers 1 lto 5 are shown outwardly .of the flange in positions corresponding with their stamped locations on the flange. The coils of each of the geophones will be assumed to be .connected to corresponding pairs of jacks. For example. the coil B5. diagrammatically shown in Fig. 9, is connected to the 11 jacks 55a and 55h. These jacks (nearest the numeral 1) will be identified with the code marking A. Corresponding numerals and letters appear on each geophone assembly in like loca-- tions.

For a surveying system in which signals from each geophone are to be separately transmitted to the recorder, the plug-contact assembly including the flange 21a of each section of the cable will be assembled with respect to each geophone housing in a diiferent angular position. For this purpose each flange 21a, Fig. 9, is provided with a marker or index which may be conveniently in the form of a notch 81. Starting with the length of cable from boat I6, Fig. 1, the cable flange may be assembled to the housing of the geophone assembly or unit I9 with its index or notch 81 in the No. 1 position. This will connect the coil or detecting element 85 of the unit I9 to a first pair of conductors of the cable 32. The righthand flange of the cable section ISB is positioned in a like manner with its index in the No. 1 position of the lefthand flange of geophone assembly I9. The lefthand flange of cable section I9B is positioned with its index in the No. 2 position of geophone assembly I8, and the righthand flange of the cable section IBB is, likewise, assembled in the No. 2 position of geophone assembly I8, thus connecting the geophone coil of that assembly to a second pair of conductors. Similarly, the flanges of cable sections I1B, IEB, I5B and I4B are respectively associated in positions numbered 3-1 of units I1, I6, I5, I4 and I3 to connect their respective geophone coils to separate pairs of conductors. The assembly of the various flanges in the foregoing manner provides a separate electrical circuit to the recording apparatus from each coil or sensitive element of each detecting unit.

Not only has the foregoing construction the advantage of uniformity in the manufacture of geophone units, but it also provides, in field operations, an exceedingly useful and convenient switching arrangement, since if the associated cable anges are assembled to two geophone units in like positions, such as the No. l position, the two coils of those units will be connected in parallel in a circuit which extends to the recorder. Thus, in the assembly of the surveying apparatus, any two or more geophones may be readily connected in parallel for the mixing of signals therefrom.

Further to illustrate, by way of example, a system in which the geophones are connected in pairs, the geophones of each pair being in parallel, reference may be had to the cable apparatus diagrammatically illustrated in Figs. 1.0 and 11. In the cable of Fig. fourteen geophone assemblies are utilized, eight of which, the assemblies I3, ISA, I4, IIIA, I5, IBA, I9 and I9A, are shown. The cable is assembled with two of its geophones connected to each pair of its conductors. Accordingly, the left-hand flanges of the cable sections 9| and 92 are bolted to geophones I9A and I9 with their notches or indexes in the No. 1 positions; likewise, the right-hand flanges ofY cable sections 92 and 93 are bolted to geophone assemblies I9A and I9 in the No. l position. In Fig. l2 a fractional part of the righthand end of the geophone I9A is shown with the cable flange 21a assembled with its index 81 opposite the numeral 1. Similarly, in Fig. 13 the left-hand end of geophone assembly I9A is shown with the cable flange 21a assembled with its index in the No. 1 position. The right-hand ,end

of geophone assembly I9 and its cable section 92 Will be assembled as shown in Fig. 12, while the left-hand end will be the same as shown in Fig. 13. 4`As a further example as to how the cable sections are assembled, reference may be had to Figs. 14 and 15 which fractionally illustrate the associated flanges of geophone assembly I4A. The coil of geophone assembly IIIA is connected in parallel with the coil of geophone assembly I4 and to conductors leading to the jacks opposite the No. 6 position. Accordingly, the index 81 of the flange 21a of cable section 96 is opposite numeral 6 (which is upside down), and the index 81 of the flange 21a of cable section 91 is opposite the numeral 6. Similarly, the indexes of the flanges connected to the geophone assemblyV I4 are opposite the numeral 6. It will thus be seen that the desired connections of the geophones may be readily effected, it being understood the remaining pairs of geophones are similarly connected to the remaining pairs of conductors by similarly assembling cable sections'94-99- The geophone assembly I3 is sealed at itsjleft end by a disc or closure I3a.

The system of Fig. 10, as a whole, is diagrammatically illustrated in Fig. 11. The coil I9b of the assembly IBA is, of course, shown connected by conductors to a double pair of jacks identified by the letter A, one pair being at one end and the other pair at the other end of the geophone case or housing. Similarly, the coil I9c is connected to like double pairs of jacks. Since the pair of plugs of the associated cable sections located in the No. 1 position complete the connections to coils I9b and I9c, the signals therefrom are mixed in the circuit comprising the pair of conductors 20|. conductors extend from the recorder and boat (not shown in Fig. ll) throughout the cable including all fourteen geophone assemblies. Only coils I9b and I9c are connected to the pair of conductors 20|, since all other cable flanges are differently associated with the remaining geophone assemblies. More particularly, the cable flanges of assembly IBA are associated therewith, with the indexes opposite the No. 2 positions. Thus, the geophone coil I8b is connected to the pair of conductors 202. The geophone itself has in this instance been shown in detail with the housing omitted in order that the diagram as a whole may be given a greater functional meaning. To the left of that geophone the cable is shown broken away. It will be understood, however, that the next geophone coil will be connected to the pair of conductors 202, and additional pairs of geophone coils to the pairs of conductors 203 and 204. One geophone coil will also be connected in parallel with the coil I 5c and to the pair of conductors 205. switching or paralleling operations are simply accomplished by successively assembling the cable assemblies with their indexes in proper relation to the numbered positions of the flanges of the geophone assemblies. Thus, the indexes of the cable flanges associated with the geophones I4A-I4, I3A--I3, will be assembled respectiveli7 in the No. 6 and No. 'I positions of the housings in order to connect coils I4b and I4c to the pair of conductors 206; and to connect coils I3b and I3c to the pair of conductors 201.

If it is desired to mix the signals from three geophones, as from coils |811, I9c and I9b, it is only necessary to couple the associated cable sections to the selected geophone housing with vtheinlrexes,on theflanges di such cable sections It will be observed that these.

These located opposite the No. 1 positions. Thus, any geophone coil will be connected in parallel with any other coil if the indexes of the cable sections are assembled to the geophone housings in the same numbered positions. Mixing of signals from any selected group of geophones may readily be accomplished.

The general practice of utilizing several geophones in parallel for each trace is familiar to those skilled in the art and is desirable field practice for the improvement of seismic records Where there prevails a high noise level or high amplitude of spurious signals due to near surface effects. In some areas it has been found `necessary to use ten or more geophones per trace in order to distinguish reflections over noise While the geophones may be of any suitable type, a geophone of the velocity type is shown in Fig. 11. It comprises a magnetic structure which is provided with a central pole piece |0|. A plurality of turns of wire forming the coil |8b are wound on a spool or form |03 which is resiliently mounted by springs |06 axially of and complementary with the central pole piece 0|. Coil |8b is terminated in glass-seal terminal posts |05 which extends through a. hermetically sealed enclosure |06 for the assembly. This device may be taken as illustrative of vone of several types of geophones or vibration-sensitive devices now in use, and which may readly be adaptable to the system of this invention.

In utilizing the method and apparatus of the above-described modification of the invention, it has been found that the cable comes to rest upon the ocean floor with the longitudinal axis sufficiently horizontal as not to require compensation for deviation of each geophone from the horizontal. For applications in which corrections should be made, a double-gimbal mounting may be utilized so 4that the geophone unit itself will remain vertical regardless of the position of the geophone housing. Such a mounting is shown in Fig. 16 wherein the bottom-heavy cradle 58 of Figs 2 and 3. with the detector 30 nested therein, is mounted on a ring provided With pivots |2 and H3, providing a rotational axis perpendicular to, and intersecting, the pivotal axis of the cradle 58. More specifically, the bottom-heavy cradle 58 of Fig. 16 has its anti-friction bearings E0 and lcarried by mountings H0, forming a part of the gimbal ring The ring is provided with pivots or shafts which are mounted in the geophane case in the same manner as are shafts 62 and 63 in the construction of Fig. 2. Shafts 62, 53, ||2 and I3 are provided with electrical paths for transferring signals generated by geophone 30 through the axis of rotation to the jacks carried by the housing (not shown in Fig. 16). arrangement includes conductors and 5|, insulated plug arrangement (not shown, but similar to plugs 43 and 52 of Figs. 2 and 3), springbiased plunger It, conductors H5 and insulated plug H6, shown in section at the left of Fig. 16.

The construction so far described is characterized by the provision of the interchangeable geophone units and the interchangeable cable sections. Such a construction embodying the fea- The electrical path of the double-gimbal tures of the present invention eliminates many problems which would otherwise arise in the field, provides for many contingencies, and permits a wide variety of operating methods to meet widely varying conditions. Such an arrangement em;- b'o'dying the present invention is particularly desirable for underwater exploration, since in the course of time, -it is possible that certain geophones or cable :sections may be damaged by sharp coral format-ions or by obstacles lencountered during the towing -of the spread from one location to another. Thus, when any unit fails or when the abrasion-resistant covering is broken, repairs may be quickly and readily effected in the field. These advantages have proven so ydesirable as to dictate the described construction as the preferred one, though, of course, a surveying .apparat-us within the scope of 'the invention may be wholly assembled at the factory and wholly hermetically sealed without provision for repairs other than by opening up vulcanized coverings and-the like.

In any case, the surveying appara-tus is of .a relatively streamlined lcharacter to minimize impalement upon, 'or the wedging into, vsub-'surface obstacles which would otherwise prevent ready movement thereof from Aone location to another.

It is entirely free of branches, divisions, vextensions and any unwieldy appending components which would readily lodge behind and jam in underwater `obstacles rough in character.

In summary, it has been found that with a surveying apparatus of the character disclosed, underwater surveying can be accomplished in less time over a given area than heretofore has been required in land surveys, and there has been avoided the need to discontinue operations when the waves are higher than those permitting smallboat operation. Moreover, there is assured the uniform placement of each geophone in a straight line with equal spacing therebetween. There has been found the further advantage that the towing of the cable-geophone assembly from one location to the other, particularly in a sandy or muddy bottom, embeds the cable and assemblies into the bottom, keeps them generally horizontal, and assures Aefficient transmission of the seismic signals from the earth to the geophone housing for production of seismic signals of amplitude higher than would be expected on dry land with comparable Iconditions of operation.

Though a preferred embodiment of the invention has been disclosed in detail, it is to be understood that further modifications within the scope of the appended claims may now suggest them selves. Y.

What is claimed is:

1. In a seismic surveying apparatus, the combination of a, geophone housing, a first gimbal ring within and rotatably supported by said housing, a second gimb-al ring supported by said first gimbal vring and having an axis of rotation perpendicular to and intersecting the axis of rotation of said first vgimbal ring, a seismic detector supported-in said second gimbal ring, said second gimbal ring being gravity biased to maintain -said detector ina vertical position regardless of the vposition of said housing, a pair of contacts carried by said secondy gimbal ring co-axially of its axis of rotation and connected to said detector, insulated spring-biased contact plungers engaging said contacts, insulated contacts vcarried by said first gimbal ring co-axially of its axis of rotation and connected to said plungers, and insulated spring-biased contact plungers engaging said second vinsulated contacts for transmission thereto of 'signals from said detector.

2. In a vseismic surveying apparatus, the combination of a first gimb'al ring, means for pivotally supporting said ring, a, second gimbal ring supported by said first gimbal ring and having an of rotation perpendicular to and intersecting the axis of rotation of said rst gimbal ring, a

seismic detector supported in said second gimbal ring, said second gimbal ring being gravity biased to maintain said detector in a vertical position regardless of the position of said supporting means, a pair of contacts carried by said second i gimbal ring co-axially of its axis of rotation and connected to said detector, insulated springbiased contact plungers engaging said contacts, insulated contacts carried by said first gimbal ring co-axially of its axis of rotation and connected to said plungers, and insulated springbiased contact plungers engaging said second insulated contacts for transmission thereto of signals from said detector.

3. In a seismic surveying apparatus, the cornbination of a geophone housing, a first gimbal ring within and rotatably supported by said housing, aV second gimbal ring supported by said rst gimbal ring and having an axis of rotation perpendicular to and intersecting the axis of rotation of said first gimbal ring, each said ring having a pair of contacts in abutting relation along a diametral line thereof coincident with the axis cf rotation, a seismic detector supported in said second gimbal ring, said second gimbal ring being gravity biased to maintain said detector in a vertical position regardlessof the position of said housing, a pair of relatively movable contacts located at the pivotal axis of each ring, and conductors interconnecting said detector and the contacts at the axis of said second gimbal ring and additional conductors interconnecting the contacts at the axes of both of said rings for completing an electrical circuit from said detector through the contacts carried by said second gimbal ring and then through the contacts carried by said irst-named gimbal ring.

4. A seismic surveying cable comprising the combination of a plurality of cable sections, a rigid housing interposed between adjacent cable sections within which is mounted a geophone, each said cable section comprising (a) a rigid fitting, (b) at least one tension-bearing member mechanically secured to said fitting, (c) a plurality of insulating electrical conductors extending through said fitting and into the interior of said rigid housing, sealing means between said iitting and said housing comprising a packing recess, packing disposed therein and means for subjecting said packing to compression to expand the same radially of said packing recess and radially of said inwardly extending electrical conductors to place them and their insulation under compressive forces to form watertight seals to prevent ingress of moisture toward said housing, a flange secured to said fitting, and means for securing in watertight relation said flange to said rigid housing, the location of said watertight seal about said extending conductors being spaced a substantial distance from the end of said tting to prevent movement of said inwardly extending conductors in the zone of said watertight seal upon flexure of said cables in a region outwardly of said fitting.

5. A seismic surveying cable comprising the combination of a plurality of cable sections, a rigid housing interposed between adjacent cable sections within which is mounted a geophone, each said cable section comprising (a) a rigid tting having an elongated end portion, (b) an abrasion-resistant sheath in telescopic relation with and tightly secured to said end portion, (c) at least one tension-bearing member mechanically secured to said fitting, (d) a plurality 'of insulating electrical conductors Vdisposed within said abrasion-resistant sheath and extending through said fitting and into the interior of said rigid housing, sealing means between said tting and said housing comprising a packing recess, packing disposed therein and means for subjecting said packing to compression to expand the same radially of said packing recess and radially of said inwardly extending electrical conductors to place them and their insulation under compressive forces to form watertight seals to prevent ingress of moisture toward said housing, a iiange secured to said fitting, and means for securing in watertight relation said ange to said rigid housing, the location of the watertight seal about said conductors being spaced a substantial distance from the end of said fitting to which said sheath is secured to prevent upon flexure of said cables in a Vregion outwardly of said fitting movement of said inwardly extending conductors at said location of said watertight seal.

6. In a seismic surveying apparatus, the combination of a geophone cable including a housing, a rst gimbal ring, pivotal supports for said ring rotatably supporting it within said housing with the axis of rotation of said gimbal ring extending along the axis of said housing and of said cable for rotation of said housing and of said cable about the axis of said gimbal ring, a second gimbal ring, pivotal supports for said second ring rotatably supporting it from said first gimbal ring for rotation about an axis perpendicular to that of said rst gimbal ring and perpendicular to the longitudinal axis of said cable, a seismic detector rotatably supported in said second gimbal ring and gravity-biased to maintain said detector in a vertical position during rotation of said housing about its longitudinal axis and during tilting of the housing along its axis, an electrical circuit extending from said detector first through the axis of rotation of said second gimbal ring and then through the axis of rotation of said first gimbal ring, said circuit at each pivotal mounting of each gimbal ring including butt contacts for maintaining said circuit without imposing restraint upon rotation of either of said gimbal rings, and electrical conductors in said cable connected to the conductors extending outwardly of the pivotal supports of said first gimbal ring.

GOETHE M. GROENENDYKE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,470,733 Hayes Oct. 16, 1923 2,019,497 Kuntze Nov. 5, 1935 2,021,330 Ross et al Nov. 19, 1935 2,027,393 McCreary Jan. 14, 1936 2,191,120 Slichter Feb. 20, 1940 2,191,121 Slichter Feb. 20, 1940 2,241,428 Silverman May 13, 1941 2,283,200 Flu'de Mar. 19, 1942 2,324,378 Flude July 13, 1943 2,407,697 Williams Sept. 17, 1946 2,410,805 Black Nov. l2, 1946 2,423,591 Flude July 8, 1947 2,426,657 'Williams Sept. 2, 1947 2,440,903 Massa May 4, 1948 FOREIGN PATENTS Number Country Date France June 7, 1926 

